$729$ small identical spheres each charged to an electric potential $3 \ V$ combine to form a bigger sphere. The electric potential of the bigger sphere is (in $V$)

$A$ pellet carrying a charge of $0.5 \, C$ is accelerated through a potential difference of $2000 \, V$. The kinetic energy attained by the pellet is:

Two electric charges of $9 \mu C$ and $-3 \mu C$ are placed $0.16 \ m$ apart in air. There will be a point $P$ on the line joining the two charges and between them where the electric potential is zero. The distance of $P$ from the $9 \mu C$ charge is: (in $m$)

Four electric charges $+q, +q, -q$ and $-q$ are placed in order at the corners of a square of side $2r$. The electric potential at a point $P$ midway between the two negative charges is:

The diagram shows a small bead of mass $m$ carrying charge $q$. The bead can freely move on a smooth fixed ring placed on a smooth horizontal plane. In the same plane,a charge $+Q$ has also been fixed as shown. The potential at point $P$ due to $+Q$ is $V$. The velocity with which the bead should be projected from point $P$ so that it can complete a circle should be greater than:

$A$ small conducting sphere of radius $r$ is lying concentrically inside a bigger hollow conducting sphere of radius $R$. The bigger and smaller spheres are charged with $Q$ and $q$ respectively $(Q > q)$ and are insulated from each other. The potential difference between the spheres will be